Date Approved

7-8-2025

Graduate Degree Type

Project

Degree Name

Medical Dosimetry (M.S.)

Degree Program

Allied Health Sciences

First Advisor

Xuanfeng Ding, Ph.D., DABR

Second Advisor

Kristen Vu

Academic Year

2024/2025

Abstract

Purpose

There has been a tremendous interest in applying Spot-scanning Proton Arc (SPArc®) to benefit head and neck cancer (HNC) patient population. However, the dental hardware materials effects on the beam distribution are not well understood, and placing spots through the dental hardware may cause an unnecessary degradation of target coverage if the material components differ from the nominal plan. The purpose of this study is to provide a quantitative dose perturbation analysis of the uncertainties caused by dental hardware and introduce a SPArc® planning strategy to mitigate such impacts.

Methods and Materials

A published in-house developed SPArc® optimization algorithm was used to generate two different proton arc plans. The algorithm includes control point resampling, energy layer redistribution, energy layer filtration, and energy layer (EL) resampling. The nominal Spot-scanning Proton Arc dental avoidance (SPArcdental-avoidance) plan introduced an avoidance sector between 300 and 60 degrees to prohibit the proton spots from entering through the dental hardware. Nominal SPArc® plans (SPArcoriginal) were generated without the dental hardware avoidance sector. In the nominal SPArcoriginal and nominal SPArcdental-avoidance plans, dental hardware was overridden as titanium (physical density 4.54 g/cm³). In the dose perturbation evaluations, the dental hardware was overridden to stainless steel (physical density 7.95 g/cm³), for the SPArcdental-avoidance and SPArcoriginal perturbation plans. Dose perturbations were evaluated in terms of OARs dose sparing and target coverage to quantitatively assess the plan’s robustness in case of such material density uncertainties compared to the nominal plans.

Results

The study found there is no statistical difference between nominal SPArcoriginal and nominal SPArcdental-avoidance planning in terms of OARs dose sparing, CTV coverage, and conformity index. There is a statistically significant difference in CTV coverage between titanium and stainless-steel density in the nominal SPArcoriginal and perturbed SPArcoriginal (D95:P =0.0391, Δ=±0.04Gy). There is also a statistically significant difference in dose to OARs in the nominal SPArcoriginal and perturbed SPArcoriginal for left parotid (P =0.0156 Δ=±0.04Gy), right parotid (P =0.0078, Δ=±0.05Gy), and muscular constrictors (P=0.0215, Δ=±0.09Gy). The only statistically significant finding between nominal SPArcdental-avoidance and perturbed SPArcdental-avoidance was the dose to the muscular constrictors (P =0.0156, Δ=±0.03Gy).

Conclusion

This is the first SPArc® study to evaluate the dosimetric perturbations associated with treating HNC patients with dental hardware. The results show a statistical significance between SPArcoriginal in terms of target coverage and OAR doses when changing the hardware density. Meanwhile, the SPArcdental-avoidance showed no statistical significance regarding target coverage and had minimal OARs with a statistical significance when changing the dental hardware density. However, as the difference is marginal, there is no clinically significant difference between these two due to the planning strategy of protecting the oral cavity. In our opinion, both planning strategies work for bilateral HNC with hardware in clinical practice and should be evaluated on a case-by-case basis.

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